The present invention relates to a novel developing agent for color photography and more particularly it relates to an improvement in p-phenylenediamine type developing agents which are used with couplers to form color images.
The color developing solution used for color development after color photographic material is exposed contains (1) a color developing agent which reduces silver halide and simultaneously is oxidized to cause coupling reaction with coupler to form color, (2) a preservative such as sodium sulfite, hydroxylamine, etc. which prevents the developing agent from being deteriorated due to oxidation with air, (3) a buffer which stabilizes the developing solution at a high pH to obtain a high developing activity, (4) an anti-fogging agent, and (5) benzyl alcohol for acceleration of the coupling reaction. Moreover, the developing solution may contain polyethylene glycols, surfactants, auxiliary developers. etc.
In the color development, the exposed silver halide is reduced to silver by development and on the other hand the developing agent is oxidized to form an oxidation product of the color developing agent, which effects coupling reaction with coupler under alkaline conditions to form a color image. It is known to use p-phenylenediamine derivatives as color developing agent for obtaining a color image using the oxidizing ability of said exposed silver halide.
However, not all of silver halide particles having a latent image are developed into silver and in order to obtain an image of high quality it has been demanded to provide a color developing process which can increase the ratio of the produced dye to the exposed silver halide than the conventional developing agent. Furthermore, recently it has been demanded to provide photographic developing solution from which benzyl alcohol which has been used for acceleration of development is omitted to prevent environmental pollution. However, development with the conventional developing agent without benzyl alcohol resulted in extreme reduction in density. By use of the color developing agent of the present invention, color images which have sufficiently excellent density and show substantially no change in hue can be obtained regardless of the presence of benzyl alcohol.
Moreover, the procedure for preparing color developing solutions by weighing various components of the developing solutions in correct proportions and dissolving them requires long time and great power of man. Therefore, developing solutions previously prepared in correct proportions have been demanded. A method by which color developing solutions can be obtained only by mixing several kinds of components and diluting them is very advantageous. However, from the point of transportation, a high concentration of the developing solution is required and so it is required that the color developing solution has a high solubility.
It is also desired that the color images formed by the coupling reaction are stable for a long period of time under exposure to heat, light and high humidity.